"Extra" (non-existant) roads

FoggArea

Posted 15 February 2010 - 01:35 AM

FoggArea

Newbie

New Member

1 posts

United States

I have loaded several roads shapefiles and I am astounded that they each show roads in and around my neighborhood that do not actually exist. I have lived here for over 25 years and these roads did not exist when I moved in. A more curious fact is that more recent the file the worse the problem is. (The more recent, the more non-existent roads there are.) I have asked my friends to spot check their neighborhoods and they each of them found "extra" roads around their homes too. So the problem seems to be wide spread.

I have looked at the individual fields and I cannot find any data that would differentiate the non-existent road from roads that actually do exist.

The problem exists in the TIGER data, the ESRI data and data from my state’s (Connecticut) GIS database. (Which is no surprise really since they get data from the TIGER database.)

So….
1) I am the only one that has noticed this,
2) Does anyone know how to weed out the extraneous roads

or

3) Can anyone suggest a reliable source of accurate road information. (I am doing this as a volunteer for a small non-profit organization to map their hiking trails, so price is a factor.)

Posted 15 February 2010 - 04:31 AM

Nick H

Posted 15 February 2010 - 05:07 AM

Nick H

Legendary Contributor

Validated Member

307 posts

Gender:Male

Location:Caversham, Reading, England.

United Kingdom

...2) Does anyone know how to weed out the extraneous roads...

One way of checking for phantom features would be by converting the shape files to KML and viewing them in Google Earth. This isn't hard to do and it makes checking very easy. It would also give you a very good indication of the quality of the shape files.

Charles Syrett

Posted 15 February 2010 - 09:29 AM

Charles Syrett

Ultimate Contributor

Validated Member

540 posts

Canada

To answer your question about whether anyone has noticed this -- welcome to the wonderful world of street mapping! One of the essential activities in preparing a street map is to edit compiled mapping sources so that:

1. Streets that are nonexistent are deleted, and

2. Streets that do exist are added, from whatever source can be found.

All source material has this problem, and it always has, even long before GIS was invented.

Another thing: Just because the source shows two streets intersecting, doesn't mean they actually do. Sometimes the municipal authorities will deliberately seal off access with a curb, sidewalk, and/or planter. To make things even more interesting for us cartographers, sometimes these obstructions are almost impossible to see on air photos, even when you zoom in. But they can sure as heck be seen by someone driving there and using your map!

You could almost define a cartographer as someone who likes this "problem" on all source material, and likes correcting it!

As for how to deal with it -- that's why the field of cartography exists, and always will, despite Google Maps etc! (It's like asking a doctor, "How do I deal with sickness?") There are many different ways, some of which will be unique to your particular situation. Already there are a lot of good suggestions on this thread, but ultimately you just have to dig in and start having fun witb it!

I have loaded several roads shapefiles and I am astounded that they each show roads in and around my neighborhood that do not actually exist. I have lived here for over 25 years and these roads did not exist when I moved in. A more curious fact is that more recent the file the worse the problem is. (The more recent, the more non-existent roads there are.) I have asked my friends to spot check their neighborhoods and they each of them found "extra" roads around their homes too. So the problem seems to be wide spread.

I have looked at the individual fields and I cannot find any data that would differentiate the non-existent road from roads that actually do exist.

The problem exists in the TIGER data, the ESRI data and data from my state’s (Connecticut) GIS database. (Which is no surprise really since they get data from the TIGER database.)

So….1) I am the only one that has noticed this,2) Does anyone know how to weed out the extraneous roads

or

3) Can anyone suggest a reliable source of accurate road information. (I am doing this as a volunteer for a small non-profit organization to map their hiking trails, so price is a factor.)

loximuthal

Posted 15 February 2010 - 09:32 AM

loximuthal

Master Contributor

Validated Member

102 posts

Gender:Male

Location:Bowie, MD

United States

As a Census cartographer I work with TIGER files (source of the TIGER/Line files) every day, and can tell you that there are many feature errors there, not just streets. As a percentage of features I believe it is actually quite small, but when the overall size of the database is as large as it is, even a small percentage works out to a sizable number. We work hard to fix problems whenever we find them, and work with local jurisdictions on several programs to take advantage of their local knowledge, but the level of particpation varies widely, the quality of our inputs varies also, and sometimes automated processing of a nation's worth of data causes some oddities to crop up. The non-existent roads in your neighborhood could be either new introductions (newly planned roads), left over from the initial creation of TIGER (mid-80s) that never got cleaned up, or bad updates. Not that it matters for your purposes.

None of that helps you with your problem, but Census does know about the data quality issues. We are even trying to get a budget item approved to work on a comprehensive quality improvement program. So maybe in a few years the next TIGER/Line files will be look better for your neighborhood

Posted 15 February 2010 - 10:31 AM

I have little to add to this discussion other than to agree with the above posters that the problem is indeed widespread and present on most source maps (city or county base maps and tiger files in particular). As an aside, they are often referred to as "paper streets", because they exist only on paper. Many if these are historic, now grown over trails or roads but just as many or more are roads that were planed but never built.

jbl

Posted 15 February 2010 - 01:36 PM

jbl

Contributor

Validated Member

27 posts

Location:JoCo_KS

United States

I guess that I really cannot ad much to whats already been said.
I live in Johnson County, Kansas and even the 2009 Tiger files were missing many roads, some important arterials.
I called the Census dept and reported the fact that there were many errors and as I remember they said that they would try to review it. Yeah, right!
The adjoining county to the east is Jackson County, MO and it is accurate to maybe 99%. Go figure.

As far as :

3) Can anyone suggest a reliable source of accurate road information. (I am doing this as a volunteer for a small non-profit organization to map their hiking trails, so price is a factor.)

Without a source for more accurate data, or expensive 'pay data' just compare to Google Earth, Google Maps, Bing, both street and Hybrid (satellite+streets).

If necessary you can get screen shots of small extents and georeference them into your shp file for comparison.

ki0eh

Posted 16 February 2010 - 03:44 PM

1) I am the only one that has noticed this,2) Does anyone know how to weed out the extraneous roads

or

3) Can anyone suggest a reliable source of accurate road information. (I am doing this as a volunteer for a small non-profit organization to map their hiking trails, so price is a factor.)

That's why I do a lot of my mapping, and it's a big problem as the other posters have noted.

One tactic that might work is trying to get an in with emergency managers in your area. Perhaps someone in your organization knows someone who knows someone in your local emergency management agency. Sometimes they have much better road data than even the Navteq/Tele Atlas folks.

Have you contacted the town GIS people? Often after they warm up to you and realize that you are working with a penniless non-profit, the data CD that they sell for $1,000 or more to engineering firms, might wind up in your hands.

Hopefully your mapping covers a small enough region that you can just edit whatever kinda close source data you can find, by heads-up digitizing on high resolution airphotos.

When all else fails, plant a logo, legend box, or north arrow over an especially offending section of basemap info that's not critical enough to fix.